You can see I've made a bit more progress on the scarf. The color of the scarf in the pictures is DARKER than how it looks in real-life. I'd suggest that if you're going to use Knit Pick's Andean Silk for your Gryffindor scarf, choose "Barn Red" instead of "Hollyberry". I'm using the latter and it's a little too cheerful for me.
As for the "Mustard" stripes, I'm getting a little better at the joins:
You can see the jog where the yellow yarn starts and ends. I'm not too bothered because I'll block the scarf so that the jogs are along the edge. I'm not cutting the yellow yarn for every new double-stripe, but am instead carrying the yarn up the inside of the scarf. I'm doing this for two reasons: (1) Less yarn used (2) Fewer ends to weave in. The only problem with this is getting the joins to be nice and smooth. Whatever, this scarf project is a learning experience.